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Researchers find hearing important
for safe-driving performance by truckers

By Liz Crumbley

Spectrum Volume 20 Issue 08 - October 16, 1997

Hearing tests are important to the safe performance of truck drivers, Virginia Tech researchers have told the Federal Highway Administration (FHWA), which is re-evaluating the hearing requirement for interstate commercial drivers.
Principal investigators John Casali, the Grado professor and department head of industrial and systems engineering (ISE) at Tech, and Gary Robinson, senior research associate, received a FHWA research contract to determine if the hearing requirement is necessary and effective. The study was carried out in the Auditory Systems Laboratory of ISE's Human Factors Engineering Center.
Currently, Robinson explained, the FHWA requires drivers to take one of two hearing tests: a "forced-whisper" test conducted by a medical examiner who stands five feet behind the driver and whispers, or pure-tone audiometry, in which the driver listens through earphones for pure tones produced by an audiometer.
To evaluate the current FHWA requirement, Robinson, Casali, and Ph.D. student Suzanne Lee performed an extensive task analysis, beginning with interviews of truck drivers, dispatchers, mechanics and other commercial driving experts. The results of these interviews were used to devise questionnaires that were distributed to 80 truck drivers, who provided information about driving tasks that require hearing.
Drivers' responses, which included reports of highway incidents involving hearing, indicated to the ISE researchers that hearing is critical to safe performance.
To quantify noise levels in truck cabs, Lee traveled with drivers in several trucks and conducted spectral noise measurements under different conditions, such as with the radio on and off and windows up and down. "We wanted to measure the best- and worst-case hearing scenarios," Robinson said. Lee also measured the levels of sounds that drivers must listen for, including train horns, sirens and in-cab auditory signals.
When compared with previous studies reported in the literature, these measurements indicated that the overall sound pressure level (SPL) in truck cabs has decreased during the past 30 years due to a concerted effort on the part of truck manufacturers to isolate the cab from the engine, which is the primary source of noise. However, the overall SPL still is relatively high--an average of 89.1 decibels over eight highway-speed driving conditions, Robinson said.
The trucks monitored in the ISE study were all 1992-1997 conventional-cab models (as opposed to cab-over models) with sleeper berths, representing three manufacturers.
Using the collected noise and signal spectra data, the researchers calculated the masked thresholds--or minimum sound levels required for hearing--for each signal in each of the different noise conditions. Robinson, Casali and Lee used these minimum hearing levels as the basis for their recommendations to the FHWA for hearing requirements. "Our study produced the first empirical data to show what levels of hearing are required for safe driving," Robinson said.
Robinson said the ISE study reached two major conclusions. First, the FHWA needs to retain the hearing requirement for commercial drivers, who need to hear certain signals and sounds to drive safely, and also need to communicate via radio and telephone. Second, the driver hearing test should be the pure-tone audiometry rather than the forced-whisper test, which is not well-defined.
Robinson said the FHWA will review the study before deciding whether to use it in modifying the current requirements. If implemented by the federal agency, Casali said, the recommendations of the Virginia Tech research team will affect licensing requirements for truckers in a way that should ultimately improve trucking safety.